A surface acoustic wave device converts electrical energy into acoustic wave energy or converts acoustic wave energy into electrical energy. For example, the surface acoustic wave device, as shown in FIG. 1, includes a piezoelectric substrate 10, bus bars 21 and 22 formed on the substrate 10 to be opposite each other, and inter-digital electrodes 31 and 32 connected to the bus bars 21 and 22 respectively to be alternately arranged.
One of problems of the surface acoustic wave device is an unnecessary transverse mode. The transverse mode generates spurious responses, causes undesirable ripples, or increases an insertion loss. This phenomenon has a bad influence on properties of the surface acoustic wave device.
As one of methods for suppressing a transverse mode in a surface acoustic wave device, document titled “Design Modeling and Visualization for Low Transverse Modes R-SPUDT devices” provides a so-called piston mode in which a wave velocity reduction region is added to an edge of a transducer to generate a mode in which a velocity is regular at an opening and becomes reduced as getting toward the outside. However, it is difficult to embody a structure disclosed in the document due to a complicated pattern and there is a high possibility that a failure occurs.